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Date:      Fri, 24 Apr 1998 10:14:37 +0200 (MET DST)
From:      Luigi Rizzo <luigi@labinfo.iet.unipi.it>
To:        gurney_j@resnet.uoregon.edu
Cc:        current@FreeBSD.ORG
Subject:   Re: Bridging...
Message-ID:  <199804240814.KAA20818@labinfo.iet.unipi.it>
In-Reply-To: <19980424005740.35254@hydrogen.nike.efn.org> from "John-Mark Gurney" at Apr 24, 98 00:57:21 am

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> Luigi Rizzo scribbled this message on Apr 24:
> > I am trying to see what could be the best way to implement bridging
> > within FreeBSD. The main app would be to connect 10/100 Mbit
...
> think, FreeBeSwitcheD on a floppy... :)

actually, i have been using pc-based bridges (with code derived
from netboot) for a long time -- look at my web page and search for
PCbridge 3 . The code compiles on FreeBSD and can be run off a floppy
or an EPROM.

>From the point of view of efficiency this is better since with certain
hardware it does not need to transfer the whole packet to main memory,
but only the interesting parts -- headers etc. . Since the bus
bandwidth is often the bottleneck for ISA cards, this is very efficient.

The negative side is that the netboot only support a limited set of
adapters, and no 100Mbit unit. So it would take a lot of work to port
the driver to make it work with netboot, and it would need a lot of
mainteinance with newer hardware.


> it shouldn't be to hard to keep track of what interface has what hardware
> address...  and it wouldn't have to be limited to ip either...  and think,
> an 8meg machine could support up to 400k machines...  which is a bit
> better than most switches support...

the filter needs not to be precise. PCbridge uses a small (64K) hash
table with room for 8k different addresses. When you have a conflict
you simply forward on all interfaces. In the five years i have been
using this code i have never had a problem with leaks.

	cheers
	luigi
-----------------------------+--------------------------------------
Luigi Rizzo                  |  Dip. di Ingegneria dell'Informazione
email: luigi@iet.unipi.it    |  Universita' di Pisa
tel: +39-50-568533           |  via Diotisalvi 2, 56126 PISA (Italy)
fax: +39-50-568522           |  http://www.iet.unipi.it/~luigi/
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